1. Field of the Invention
The present invention is broadly concerned with improved extrusion processes for producing engineered ingredients designed for incorporation into animal feeds or human foods. More particularly, the invention is concerned with such processes wherein separate dry and byproduct slurry fractions are initially preconditioned, followed by extrusion thereof and final drying to obtain the engineered ingredients, which may be used in lieu of conventional meat or plant-based meals heretofore produced in rendering plants.
2. Description of the Prior Art
Animal- and plant-derived byproducts, such as waste materials from slaughterhouses, supermarkets, butcher shops, restaurants, feed lots, ranches, dairies, are commonly processed in rendering plants. In such facilities, the incoming byproduct or waste materials are finely chopped and heated, either continuously or on a batch basis, which separates fats and removes water to create concentrated products. After cooking, the materials are typically screened and then dried, to create finely divided meals. The rendering process kills bacteria, viruses, parasites, and other organisms. However, owing to the generally unsanitary conditions within rendering plants, the final meal products are prone to re-contamination after fabrication thereof. Generally speaking, meat meals produced in rendering plants contain around 50-85% crude protein, 1-15% crude fat, 1-4% crude ash, and have a moisture content of 7-10% by weight.
Rendering plants can present significant environmental problems and are energy-intensive to operate. For example, the handling and processing of organic and raw materials produces significant amounts of undesirable, biodegradable elements which can lead to water and air pollution. Effective control of these problems requires sophisticated treatment processes and control equipment (e.g., water and air emission systems), which require significant capital and plant-operating costs.
For all of these reasons, in recent years the cost of rendered ingredients designed for incorporation into animal feeds, such as meals of meat, bone, fish, and blood, have increased significantly. Moreover, in certain cases, the availability of such ingredients has become problematic.
Extrusion processing is a well-established science and generally involves initially preconditioning starting ingredients to moisturize and at least partially cook the ingredients, followed by passage of the preconditioned material into and through an elongated barrel equipped with helically flighted extrusion screw(s) and an endmost, restricted orifice die. In the extruder, the material is subjected to increasing levels of heat, pressure, and shear, in order to cook the material to the desired extent. The extrudate issuing from the die is typically cut by a rotating knife to provide a chunk-type product. Extrusion technology is widely used in the production of pet and human foods.
A limitation upon extrusion processing has been that high-moisture starting products are difficult or impossible to extrude. For example, in prior practice, it has been difficult to successfully extrude starting materials having moisture contents above about 40% by weight.